Honestly, how did parents (dads) first think of this? It's like: Hey, I've got an idea. This peaceful little two-month old infant looks like he wants to go for a ride. Does he want to keep hanging in out in the warm, fuzzy vibrating chair where he's pretty much incapable of breaking? Nah. Let me just scoop him up, raise him over my head, and make him fly like an airplane. It sure makes me smile.
When my son was this age, I'm pretty sure I walked around carrying him at three feet max off the ground. I figured that way, even if I did drop him, things would probably work out ok. The post-partum period + a fear of heights = a perfect recipe for extreme anxiety.